Paper SS+OX-WeM12
A Novel 2-D Cu-Tungstate (CuWO_x) Phase on Cu(110)

Wednesday, October 31, 2012, 11:40 am, Room 22

We explore the feasibility to fabricate W-oxide nanostructures on metal surfaces via self-assembly and condensation of (WO₃)₃ clusters, deposited directly from the gas phase: here we report the formation of a novel two-dimensional Cu-tungstate CuWO_x phase on Cu(110). A beam of (WO₃)₃ cluster molecules, formed by sublimation of WO₃ powder at ~900-1000°C in a thermal evaporator, has been directed onto a Cu(110)2x1-O surface oxide at low temperature and the surface has been annealed subsequently at 600 K. At low temperature (< 15 K) the (WO₃)₃ clusters adsorb in intact molecular form , albeit in a somewhat distorted cluster geometry [1]. Upon heating to 600K, the (WO₃)₃ molecules dissociate and react with the Cu-O(2x1) surface oxide, forming a wetting monolayer with a well ordered incommensurate structure. The latter has been structurally characterized by high-resolution STM imaging and LEED. The chemical nature and electronic structure of this novel 2-D W-O-Cu layer has been investigated by high-resolution XPS core level spectroscopy, NEXAFS, and valence band spectra. The unusually sharp W 4f core level spectra, the specific NEXAFS fingerprint and the evolution of the valence band all suggest that this 2-D W surface oxide is of a Cu-tungstate CuWO_x type. Density functional calculations are in progress to help elucidating the physical and chemical nature of this unusual surface oxide phase.

Work supported by the ERC Advanced Grant SEPON

[1] M. Wagner, S. Surnev, M.G. Ramsey, G. Barcaro, L. Sementa, F.R. Negreiros, A. Fortunelli, Z. Dohnalek, F.P. Netzer, J. Phys. Chem. C115 (2011) 23480